1. Field of the Invention
The present invention relates to a light receiving element carrier on which a light receiving element, a preamplifier, high-frequency terminals, and so on are mounted. It also relates to an optical receiver including the light receiving element carrier as a module.
2. Description of the Prior Art
FIG. 9 is a perspective view showing the structure of a prior art light receiving element carrier disclosed in Japanese patent application publication (TOKKAI) No. 2000-58881. In FIG. 9, reference numeral 101 denotes a light receiving element, reference numeral 102 denotes a carrier, reference numeral 103 denotes a preamplifier, reference numeral 104 denotes an I/O pad, reference numeral 105 denotes an output pad, reference numeral 106 denotes a Vcc pad, reference numeral 107 denotes a Vee pad, reference numerals 108 to 112 denote carrier electrode patterns, and reference numeral 115 denotes a boding wire for connecting the light receiving element to the preamplifier.
In operation, an optical signal output from an optical fiber not shown in the figure is incident upon the light receiving element 101 by way of a lens not shown in the figure, and is converted into an equivalent electrical signal by the light receiving element 101. The electrical signal into which the optical signal is converted by the light receiving element 101 is amplified by the preamplifier 103 which is bonded to the carrier 102 made of ceramic, which is a rectangular solid, with a metal. The electrical signal amplified by the preamplifier 103 is then output from a pair of output pads 105 to the carrier electrode patterns 110 and 111. Furthermore, a power supply for the preamplifier 103 is supplied from the carrier electrode patterns 109 and 112 disposed on the carrier 102 to a plurality of Vcc pads 106 and a plurality of Vee pads 107.
The prior art light receiving element carrier of FIG. 9 has the following problems (A) to (C).
(A) When forming the carrier 102 as a module and mounting it within an optical receiver, it is necessary to dispose a lens and an optical fiber not shown in the figure in front of the light receiving element 101. However, the optical receiver s electric output terminals should be disposed so that they are flush with the carrier electrode patterns 110 and 111 connected to the pair of output pads 105 and formed on surfaces of the carrier 102 which is a rectangular solid. Therefore, the optical fiber is not flush with the electric output terminals and the height of the optical receiver is increased.
(B) Ceramic is generally used to form the carrier having the structure as shown in FIG. 9. When the amount of heat generated by the preamplifier 103 is large, it is necessary to form the carrier 103 by using expensive aluminum nitride (AlN) of a good thermal conductivity to dissipate the generated heat into a housing of the optical receiver. Thus, cheap alumina cannot be used to form the carrier and therefore the cost of the carrier is increased.
(C) Since the preamplifier 103 having a thickness is mounted on the carrier 102, a difference is caused only by the thickness of the preamplifier 103. In other words, since the pair of output pads 105 and so on formed on the preamplifier are not flush with the plurality of carrier electrode patterns 108 to 112, the length of wiring required for connecting these components with one another is increased and therefore the reflection characteristic of the pair of output pads 105 is deteriorated.
In sum, the first problem encountered in the prior art light receiving element carrier is that the optical fiber is not flush with the electric output terminals and the height of the light receiving element carrier is therefore increased when it is provided as a module.
The second problem is that cheap alumina cannot be used to form the prior art light receiving element carrier and therefore the cost of the carrier is increased.
The third problem is that the reflection characteristic of the prior art light receiving element carrier is deteriorated.